-0CA{ 



ADDENDUM. 



Mr. Morse has recently presented "Additional observations on the 

 selective reflection of salts of oxygen acids" (Washington meeting, Amer- 

 ican Physical Society, April, 1908). He chose substances in which the 

 " weight of the acid-forming element is not greater than the weight of the 

 oxygen with which it is combined." These substances are: CaC0 3 with 

 a reflection maximum at 6.6 fi; KN0 3 at 7.1 fi; AgN0 3 at 8 fi; CaS0 4 at 

 8.6 fi; KC10 4 at 9 p; CaSi0 3 at 9.2 ft; KC10 3 at 9.9 fi; KMn0 4 at 10.9 fi; 

 PbCr0 4 at 11.5 ft; and CaTiO s at 14.2 ft. These maxima lie close to the 

 line drawn through them, when plotted against the weight of the oxygen. 

 He excluded PbM0 4 , CaW0 4 , etc., because the weight of the acid-form- 

 ing element is greater than that of the oxygen present. Of course, if we 

 admit the validity of such a procedure the rule is proven; but a rule loaded 

 down with exceptions can not prove satisfactory, and much as all spectro- 

 scopists wish to establish such a simple relation between spectra of different 

 groups of compounds, it should be along lines of less arbitrary elimination. 



On the other hand, this simple atomic-weight relation seems to hold 

 for substances belonging to the same 

 group of compounds, even for re- 

 mote parts of the infra-red spec- 

 trum, as was shown by Nichols 

 and Day (Washington meeting, 

 American Physical Society, April, 

 1908). They found a band of 

 residual rays in SrC0 3 at 43.2 ft 

 and in BaC0 3 at 46.5 ft, for the 

 carbonates (see fig. 45). 



If we take the ratio of the in- 

 crease in atomic weight of the base to the position of the maximum, as 

 read from the graphs in figs. 43 to 45, the value for the group of bands 

 at 6.5 ft is about 500 to 1, at 11.5 u it is 260 to 1, and at 45 ft it is 20 to 1. 

 The graph (fig. 107) of these values appears to be an hyperbola. If such 

 a relation really exists and if the carbonates have a band in the region of 

 30 ft, corresponding to the CaC0 3 and MgC0 3 bands, then the aforesaid 

 ratio of atomic weight to position of the maximum is about 90 to 1, and 

 one would expect to find a maximum for PbC0 3 at 31.5 ft and SrC0 3 

 at 30 p. However, from the variation in complexity of the bands at 6 to 

 7 fi and in intensity of the bands at 11 to 14 ft, it is evident that it is use- 



181 



-a 



600 



O 400 



cc 



200 



10 20 30 40 SOJU 



Fig. 107. Mean position of groups of residual rays. 



